1. Field of the Invention
The present invention relates to a pressure sensor suitable in use for detecting a pressure in a combustion chamber of a vehicle engine.
2. Description of Related Art
As such a pressure sensor, there is known the one that has a configuration in which a diaphragm is located in one end portion of a case thereof, a distortion of the diaphragm caused by application of a pressure under measurement to a pressure-receiving surface thereof is transmitted through a pressure transmitting member to a sensor chip in which a distortion-sensing element is formed, and the distortion-sensing element outputs a signal depending on the transmitted distortion corresponding to the pressure under measurement. For details, refer to Japanese Patent Application Laid-open No. 7-19981, for example.
To mount the pressure sensor of the type described above on a vehicle engine, it is inserted from the pressure-receiving diaphragm side into a mounting hole of the vehicle engine leading to a combustion chamber of the engine, so that the pressure-receiving diaphragm is exposed to the combustion chamber side, and the sensor chip in which the distortion-sensing element is formed that should not be exposed to high temperature is applied with a force corresponding to the pressure in the combustion chamber through the pressure transmitting member.
The inventors of the present application proposed earlier a pressure sensor having a structure in which a sensor chip in which a distortion sensing element is formed is adhered to a thin-walled portion as a distortion section of a metal stem, so that a distortion of the distortion section due to a force corresponding to a pressure under measurement applied thereto through the pressure transmitting member causes the sensor chip to be distorted, and the distortion sensing element outputs a signal depending on the pressure under measurement. For details, refer to Japanese Patent Application Laid-open No. 2007-114094.
FIG. 4 is a cross-sectional view of such a pressure sensor mounted to a vehicle engine. In this figure, the dotted arrows indicate a heat transmission path in this pressure sensor.
As shown in FIG. 4, since a metal case J3 of the pressure sensor is in contact with a vehicle engine J5, there is formed a heat radiation path in which the heat transmitted from a combustion chamber J1 of the engine J5 to a pressure-receiving diaphragm J2 is radiated to the engine J5 through a contact portion between the metal case J3 and the engine J5.
However, there are also heat transmission paths in which the heat transfers to the sensor chip 4 through a metal stem J6 or a pressure transmitting member J7 disposed inside the metal case J3. Accordingly, there is a possibility that the temperature of the sensor chip J4 rises beyond an allowable operating temperature limit due to the heat transferring from the pressure-receiving diaphragm J2 side, causing the sensor chip J4 to malfunction.
In the structure shown in FIG. 4, the metal case J3 is divided into two components, a cylindrical metal pipe J8, and a housing J9. In assembling the pressure sensor, the metal stem J6 is fitted into an opening end of the metal pipe J8, and then they are integrated together by welding. After that, the metal pipe J8 integrated with the metal stem J6 is fitted into an opening end of the housing J9, and then they are integrated together by welding. Accordingly, most of the heat having been transmitted to the sensor chip J4 side beyond the opening end (weld portion) of the metal pipe J8, transfers to sensor chip J4 with little dissipation.